Earth2Earth geoscience seminar series
Speakers: Dr Laura Wallace (UT Astin), Dr Emily Warren-Smith (GNS Science)
Joining instructions: join via Zoom webinar or YouTube live stream
Image courtesy of L Wallace & E Warren-Smith
Abstract: The discovery of slow-motion earthquakes, or slow slip events (SSEs), at subduction zones in the last two decades has transformed our understanding of fault mechanics and earthquake occurrence. The northern Hikurangi subduction zone offshore New Zealand’s North Island has become a focal point for investigation of this phenomena, as the shallow occurrence of SSEs (<2-15 km) there enables near-field investigations of these processes. We will discuss a range of investigations being undertaken to better characterize the SSEs and related seismicity, as well as recent results from scientific drilling and seismic imaging to reveal the environment and rock types that host SSEs. We will also discuss results of recent efforts to use seafloor geodetic methods to resolve SSE processes near the trench.
Integration of seismological and geodetic observations has led to the proposal that SSEs are linked to the presence of, and fluctuations in fluid pressures within and beneath the megathrust shear zone, via a “fault valve” process. We will discuss seismological evidence using inferences of stress changes during the SSE cycle that suggests a precursory increase in fluid pressure may in fact precede megathrust rupture in SSEs. We also consider the earthquake locations alongside geophysical observations of crustal properties to identify the potential sources of fluids triggering shallow SSEs. These observations are important for future targeted efforts to monitor localised changes in fault zone properties during SSE cycles, in an effort to understand the physical controls on fault slip behaviour and episodicity.